CS270485B1 - Method of powdered polyimide production - Google Patents

Abstract

Powdered polyimides are obtained by polycondensation diesters or dianhydrides pyromellitic acids with aliphatic acids, diamines in the presence of an inert powder additives with a particle size of less than 60 µm and up to 350 ° C. Powder is obtained directly usable for stamping parts resist temperatures up to 350 ° C.

Description

The invention relates to the preparation of polyimide by solvent-free polycondensation in the presence of an inert additive.

Polyimides are polymers used for applications with high demands on thermal stability, dimensional stability and are used in electrical engineering, they are used as glass-metal seals up to 350 ° C, etc.

The chemical and physical properties of polyimides are influenced by the starting materials, the addition of the copolymer, the method of termination, the synthesis conditions, etc.

Polyimides can be prepared, inter alia, by the condensation reaction of polycarboxylic acid derivatives (ester acids, anhydrides) with diamines, provided that the steric ratios of the two components allow the imide ring to be closed. In the first part of the synthesis an ester-alkylammonium salt or acid-amide is formed from the acid and diamine derivative (according to starting materials and reaction conditions), the other part, polycondensation with imide ring formation can be performed in the presence or absence of solvent.

Polyimides of pyromellitic acid dianhydride and aliphatic diamine - C

For the preparation of polymers suitable for molding, it is desirable that the amine component be a linear unbranched amine with 9 or more carbons, or a branched amine with at least 7 carbons in the chain. Shorter chains provide rigid and brittle polymers (Edwards, W. M., et al., U.S. 2,710,853).

It has now been found that synthesis in the presence of an inert additive also yields amines with Cg polymers which can be easily processed by compression.

The present invention relates to a process for the production of powdered polyimides by polycondensation of diesters or dianhydrides of pyromellitic acid with aliphatic diamines HjN (CHjJp NHj, where n = 5 to 8), in which equimolecular amounts of diesters or dianhydrides an additive with a particle size of less than 60 [mu] m in an amount of 1 to 2% by weight (based on the final product) and subjected to polycondensation at a temperature of up to 350 [deg.] C.

Methods used for the preparation of polyimides:

. Pyromellitic dianhydride homogenized with an inert additive and diamine are used for the polycondensation. At a temperature of 140 [deg.] C., polyamide acid is formed, and further heating (up to 350 [deg.] C.) gradually closes the imide ring with the cleavage of water.

The dialkylammonium salt of pyromellitic acid diesters, prepared from pyromellitic dianhydride by diesterification with methanol and subsequent reaction with diamine, is used for the polycondensation. The resulting intermediate is powdery and can be perfectly homogenized with an inert additive. The actual polycondensation in the presence of this additive takes place again in two stages depending on the temperature, via polyamide-acid to polyimide.

Both of these processes provide polyimides that can be pressed, machined and used at temperatures of 350 ° C, but the esterification process has several advantages over the direct dianhydride process:

1) The binding of the diamine to the diester of pyromellitic acid is quantitative in methanolic solution, the heat generated by the exothermic reaction can be effectively controlled by cooling.

2) The white powder of the alkylammonium salt of pyromellitic acid diesters, formed after evaporation of methanol, can be perfectly homogenized with an inert additive. The homogenized intermediate can be stored for a longer period of time. An inert atmosphere without access to moisture is not necessary.

3) The resulting polyimide is a gray powder, does not darken in air at 320 ° C.

In contrast to the previous process, the homogenization of the starting materials for the preparation of the polyimide directly from the dianhydride, i.e. the mixing of the dianhydride-graphite mixture into the diamine, must be carried out without access to moisture, since the hygroscopic diamine causes the mixture to become wet and agglomerates to form.

CS 270485 Bl

As the polycondensation temperature is gradually increased, part of the diamine is carried out by the escaping reaction water, whereby the molar ratio of the reactants is disturbed.

The resulting polyimide has a gray-beige color and darkens in air at 320 ° C.

The moldings can be machined, the melting point of the product allows the use of the moldings in a wider temperature range. (For compacts formed as seals of quartz capillary columns in the chromatograph, the possibility of use up to 350 ° C was verified.)

When using the additive, no agglomerates or sticky products are formed, the polymer is powdery and can be easily extruded from the mold.

Of the powder additives, graphite appears to be the most preferred. The best results were obtained using the finest graphite function of 1 to 60 μm. Even the addition of 1% by weight is sufficient to form a polymer in the form of a powder suitable for compression. Extruded rollers «0 3.5 x 4 to 10 mm can be machined into a shape suitable for sealing glass or quartz capillary columns in a gas chromatograph. Similar findings were obtained using the addition of 2% by weight of a graphite fraction of 1 to 60 μm. At higher concentrations of graphite, polyimide is formed in the form of granules, from which the prepared compacts crumbled during processing.

An advantage of the process for the production of powdered polyimides according to the invention is that

- in the presence of an additive, the synthesis produces a finely powdery product suitable for direct compression in multiple molds and subsequent machining,

- the handling of the polyimide powder is easier because the polymer particles are not electrostatically charged, as is the case with the polymer without the additive,

- commercially available and inexpensive hexamethylenediamine can be used as amine components for synthesis,

- while polyimides obtained from diamines with 9 or more carbons in the molecule have a relatively lower melting point (polynonamethylene-pypomellitimide approx. 320 ° C), the use of lower diamines produces products with a higher melting point and thus usable at higher temperatures (eg polyimide prepared with hexamethylenediamine according to the invention - Examples 1 and 2 - melts with decomposition at 360 ° C).

The following examples illustrate the invention. % in the examples are by weight. .

'Example 1'

A portion of 10.9 g (0.05 M) of pyromellitic dianhydride was homogenized। with 0.16 g of graphite (sieved through a 0.06 mm sieve) and added to 5.8 g (0.05 M) of hexamethylenediamine.

The mixture was stirred under nitrogen for 1 h at 140 ° C, then the temperature was gradually raised to 340 ° C in a bath (Wood's metal) and maintained at this temperature for 2 h.

The gray-beige powder with 1% graphite melts with decomposition at 360 ° C, but darkens already in air at 320 ° C. The product can also be used directly for pressing.

Example 2

10.9 g (0.05 M) of pyromellitic dianhydride and 100 ml of methanol are metered into the reaction vessel. After gentle heating, 5.8 g (0.05 M) of hexamethylenediamine are added to the already clear solution of the pyromellitic acid diester formed and the unreacted methanol is removed. The resulting powdered intermediate (ester-alkylammonium salt) is homogenized with 0.3 g of graphite (particle size less than 60 μm) and subjected to solvent-free polycondensation.

The reaction vessel is equipped with a distillation head and a nitrogen inlet. With stirring, the mixture is heated to 140 ° C in a Wood Metal bath for 2 hours. The temperature is then raised to 340 ° C in a bath and maintained for a further 2 hours.

After cooling, the resulting gray powder containing about 2% graphite can be used directly for pressing small compacts in multiple molds. The moldings do not change their shape even at 350 ° C.

Claims (1)

OBJECT OF THE INVENTION Process for the production of powdered polyimides by polycondensation of diesters or dianhydrides of pyromellitic acid with aliphatic diamines Ε ^ Ν-ζΟ ^^ - ΝΕ ^, where n is 5 to 8, characterized in that equimolar amounts of diesters or dianhydrides of pyromellitic acid and aliphatic Z, á) - the diamines are mixed with an inert powder additive with a particle size of less than 60 [mu] m in an amount of 1 to 2% by weight, based on the final product, and subjected to polycondensation at a temperature of up to 350 ° C,